Objective: To isolate and characterize the DNA polymerases found in human milk and in human breast cancer cells. Approach: Isolation of the DNA polymerases will be accomplished using column chromatographic methods. DNA polymerase characterization studies will include: (1) Determination of template primer utilization specificities. (2) Molecular weight determinations. (3) Divalent cation requirements. (4) Antibody enzyme inhibition studies using antibody to purified human cellular type DNA polymerase I and a variety of purified primate viral DNA polymerases. (5) Determination of the ability of any isolated DNA polymerase to transcribe heteropolymeric region 60-70 S viral RNA. If a viral type DNA polymerase is isolated from some human milk samples, consideration will be given to the development of a radioimmune assay for use in extended epidemiological studies to determine the frequency of expression of this type enzyme in the human population.